The present invention relates to a proton conductor or a single ion conductor used for a device involving migration of cations or protons such as a secondary battery, a fuel battery, a hydrogen sensor, and an in vivo electrode, manufacturing methods thereof, and an electrochemical capacitor using it.
As one kind of solid electrolytes having an ion conductive mechanism, there is a single ion conductive high molecular weight film, which fixes a counter ionic species in a high molecular weight compound and migrates one ion species of cations or anions. As this single ion conductive high molecular weight film, for example, Nafion (registered trademark) developed by E.I. Du Pont in 1969 is known. Actual researches on mechanisms and the like have become activated in the 1980s. Synthesizing several ion conductors such as polyethylene glycol derivative, in which a carboxylic acid (carboxy group) or a sulfonic acid group (sulfo group) is bonded to a side chain, and a mechanism thereof have been considered. After that, as the technology related to fuel batteries has attracted attention again since environmental issues have come under close scrutiny, researches as an electrolyte film for solid electrolyte fuel batteries have become activated, and particularly in recent years, many researched have been performed.
Under such a background, currently, examination of a single ion conductor, particularly a proton conductor is still actively promoted. Wide applications of the proton conductor include not only the electrolyte film for solid electrolyte fuel batteries. Applications of the proton conductor have been expected in various fields such as barrier films for hydrogen sensor, biomimetic hydrogen migration films, materials for electrochromic display, proton conductor films for chemical reactor, and electrolyte films for proton migration type secondary battery. Many examinations including basic researches have been performed.
However, for the single ion conductor, there has been a problem that the ion conductivity is low. In the case of polyethylene glycol ion conductive macromolecule and the like, the ion conductivity is largely affected by temperature dependency of segment motion of the macromolecules, and therefore, the conductivity has not become superior to ion conductivity of liquid system. Further, with regard to the proton conductor, there has been a problem that the proton conductor is largely affected by moisture existing in the film (proton carrier), and therefore, the proton conductivity is significantly decreased due to decrease in the number of proton carrier in the range beyond 100° C., the boiling point of water, and its practically usable temperature range is limited to 100° C. or less.
Therefore, for example, an electrolyte film, which can have higher material strength and can express high proton conductivity by introducing an inorganic substance having an oxygen functional group into a proton conductive compound has been suggested (for example, refer to Japanese Unexamined Patent Application Publication No. 2001-155744). Further, a composite film, which can obtain high ion conductivity and can be used in a broad temperature range by mixing a high molecular weight compound having a lot of sulfonic acid groups and a cation transport type high molecular weight compound having low glass transition temperature has been suggested (for example, refer to Japanese Patent No. 2962360).
However, in the proton conductor described in Japanese Unexamined Patent Application Publication No. 2001-155744, though the film strength can be improved, the proton conductor still depends on moisture, moisture should be controlled in use, and therefore conventional problems cannot be resolved perfectly. Further, in the proton conductor described in Japanese Patent No. 2962360, since the high molecular weight compound is used as an ion carrier, the proton conductivity can be expressed even when moisture does not exist. However, there has been a problem that since the proton conductivity is subject to segment motion of macromolecules, and therefore, the conductivity when moisture does not exist is low, and further ingenuity is required for practical application.
With regard to cation transport functions in a nonaqueous solvent, there has been a report of a nonaqueous proton conductor using N,N-dimethyl formamide and phosphoric acid (for example, refer to W. Wieczorek et al., “Electrochimica Acta,” England, Elsevier Science Ltd., 2001, Vol. 46, pp. 1427-1438). However, since this conductor includes phosphoric acid anions, this conductor is not a single ion conductor. Therefore, in the case of using this conductor for an electrical sensor, a battery or the like, there is a problem that it is necessary to consider chemical stability and polarization reaction of anion species. Further, this conductor is a liquid binary system, and therefore, this conductor cannot be used as a formed body unless a gelatinizer or the like is added. Therefore, in the case of trying development of various applications thereof, there is a problem that applicable usage is limited.